Delete `WeakScriptModuleProxy` (#23398)
Summary:
This PR deletes `WeakScriptModuleProxy` and uses `ScriptModule` directly and moves the recursive script stuff into `torch/jit/_recursive.py`. The first commit is just moving code, the latter 2 contain the actual changes
](https://our.intern.facebook.com/intern/diff/16712340/)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/23398
Pulled By: driazati
Reviewed By: eellison
Differential Revision: D16712340
fbshipit-source-id: f907efcec59bb2694c079ab655304324c125e9bb
